The long-term goal of this proposal is to characterize the organization of the telomere during spermatogenesis. A major emphasis is to define the molecules associated with the telomere chromosomal domains in human sperm. A component of the telomere-binding protein complex (hsTBP) - with binding affinity to the ds hexanucleotide repeat (TTAGGG) telomere DNA - has been identified and proposed to participate in the attachment of the telomeres to the nuclear envelope. One of the components of hsTBP, called spH2B, is regarded as a subtype of the somatic histone H2B. Another component of hsRBP is a novel 50 kDa protein identified as p50. Based on these data, the applicant proposes the isolation, cloning, and further characterization of spH2B and p50. This approach will enable the identification of additional components of hsTBP in human spermatogenic cells and sperm. Additional studies using atomic force microscopy and whole mount electron microscopy include a structural analysis of the telomeric DNA that appears to retain its nucleosomal-like organization. The latter studies will explore whether a variation of the recently reported t-loop characteristic of the telomere in somatic cells is observed using in situ cross-linked telomeric DNA preparations of sperm. The proposed studies are regarded as important for the regulation of telomerase activity during homologous chromosomal pairing and recombination during meiotic prophase and ordered chromosome withdrawal after fertilization.